With an optical disk recording and reproducing device, each track on an optical disk is divided into a plurality of sectors, and information is recorded/reproduced on the disk sector by sector. Here, header information, such as a sector mark and address information, is recorded in each sector. The sector mark indicates a reference position of a sector and the address information the address of a sector.
The address of a sector being scanned by an optical beam is identified by reproducing the header information. This operation also enables access to the address of a desired sector.
Among recording methods for the optical disk recording and reproducing device, the following two methods, i.e. CAV (Constant Angular Velocity) method and CLV (Constant Linear Velocity) method, are well known and widely adopted. In the CAV method, data is recorded/reproduced on an optical disk in accordance with a recoding and reproduction use clock signal with a predetermined frequency while rotating the disk at a constant angular velocity. In CLV method, information is recorded/reproduced on an optical disk in accordance with a recoding and reproduction use clock signal with a predetermined frequency while rotating the disk at a constant linear velocity.
In the CAV method, while a recording density in an outer portion of a disk is lower than a recording density in an inner portion thereof, high-speed access to a desired sector is achieved. On the contrary, in the CLV method, high recording capacity is achieved as the linear recording density is constant from an inner portion to an outer portion of a disk. However, the rotating speed of the disk is controlled to keep a constant linear velocity, thereby resulting in slow access to a desired sector. Thus, the both methods have merits and demerits.
To counteract this, MCAV (Modified Constant Angular Velocity) method, which achieves an increased recording capacity of an optical disk and high-speed access to a desired sector, is suggested and put into practice. In this method, the optical disk is rotated at a constant angular velocity, and the recording area of the disk is divided into a plurality of ring-shaped zones of concentric circles so that recording and reproduction use clock signals have frequencies which increase from the innermost zone outwards.
As for access to a desired sector in an optical disk recording and reproducing device using the MCAV method, an optical beam is moved to a track belonging to the desired sector in a radial direction of the disk while stopping tracking control, and then tracking control is executed again.
At this time, if a sector being scanned by the optical beam belongs to a different zone from the desired zone whereto the desired sector belongs, the frequency of the recording and reproduction use clock signal needs to be changed to correspond to the zone by a process of trial and error in order to reproduce the header information in each sector in a track. Therefore, access time increases.
When the optical beam moves to a track in a different zone due to a tacking control failure caused by for example some defects on the optical disk, the access time also increases.